The present invention relates to a transmission, and more particularly to an infinitely variable transmission having an endless belt trained around driver and driven pulleys.
U.S. Pat. No. 4,152,945 patented on May 8, 1979 discloses an infinitely varible transmission comprising driver and driven pulleys each having its groove width variable axially by a hydraulic actuator, an endless belt of metal trained around the pulleys, a hydraulic pressure supply device for supplying a fluid pressure to the hydraulic actuators, and a device for controlling the supply and discharge of the fluid pressure to and from the hydraulic actuators, the transmission ratio of the belt being variable by varying the groove width of the pulleys.
The disclosed infinitely variable transmission is necessarily large in overall size since the device for controlling the fluid supply and discharge is disposed separately from the driver and driven pulleys. A pitot tube is disposed in a fluid groove positioned outside of a fluid pressure chamber defined behind a movable pulley cone for detecting the fluid pressure in the fluid groove. The fluid pressure on the movable pulley cone is controlled by the fluid pressure detected by the pitot tube. The use of the pitot tube makes the pipe system complex and makes it difficult for the transmission to be designed in its layout. Since the endless belt is made of metal, it must be lubricated. To this end, the fluid in the high-pressure fluid line which feeds the hydraulic actuators is partly supplied as the lublicating oil directly to the endless belt. Therefore, the hydraulic pressure pump is subject to an extra load which is required to compensate for the loss of the fluid pressure arising from the supply of the fluid pressure to the endless belt.
In the disclosed infinitely variable transmission, the deviation of the endless belt from the central line is zero at a low transmission ratio. When the transmission ratio is frequently varied between high and low ratios, the metal belt which is of high transverse rigidity suffers an undue force tending to shorten the service life of the endless belt.
The present invention has been made in an effort to solve the aforesaid problems of the conventional infinitely variable transmission.